Project Summary/Abstract Chromosome abnormalities due to meiotic errors are a leading cause of birth defects and spontaneous abortions in humans. The long-term objective of this work is to elucidate the mechanisms of meiotic pairing and to understand how these mechanisms help to ensure the fidelity of chromosome transmission from one generation to the next. A thorough mechanistic description of meiotic pairing has been hindered by the lack of appropriate in vivo tools. We have developed methods that allow the rapid capture and analysis of 3D images of chromosomal loci over time. Here we propose the use of these tools to measure the interaction kinetics between homologous and ectopic chromosomal loci. We will then explore how pairing interactions are affected by factors such as chromosome movement and compaction. Finally, we will identify structural features of the chromosome axis that limit non-specific chromosome interactions during meiosis. We will focus first on defining mechanisms by which Rec8, a structural component of the chromosome axis inhibits nonspecific chromosome interactions during meiosis. We will also carry out a mutant screen to identify other genes that suppress nonspecific pairing interactions. The results of these studies will lead to an understanding of the relationship between the structural features of chromosomes during meiosis and the forces that act upon them.